This type of flow cell is connected to a chemical solution pipe provided in a semiconductor manufacturing apparatus. A measurement light is irradiated to a sample solution through one of the optical windows of the flow cell and a transmitted light emitted from the other of the optical windows is received. Then, a concentration of a prescribed component contained in the sample solution is calculated based on a transmitted light intensity of the sample solution so that the concentration of the chemical solution is controlled.
Regarding the conventional flow cell, as shown in FIG. 10, a plurality of light transmitting members are bonded by welding or molecular bonding, etc., to be integrally molded so as to form a flow channel connecting from a solution introduction port to a solution derivation port inside the flow cell.
However, since a processing cost for the process of bonding by welding or molecular bonding is high, there is a problem that the manufacturing cost thereof becomes high. In particular, in the case where a material (such as, e.g., sapphire) having a corrosion resistance against a chemical solution such as hydrofluoric acid (HF) is used, since a processing cost of the sapphire is expensive in addition that the material per se is expensive, the manufacturing cost further becomes higher. Also, since the light transmitting members are bonded to each other, a cell length of each flow cell is fixed. Therefore, if it is desired to measure a concentration of a solution using a different cell length, it is needed to prepare a different flow cell and there arises a problem that the cost is raised in addition.
In contrast to this, as disclosed in Patent Literature 1, it is considered to assemble a flow cell by sandwiching the light transmitting members instead of bonding the same. Specifically, a pair of light transmitting parts are arranged to be opposed at a predetermined interval and a spacer is interposed between the pair of the light transmitting members in order to define the interval to be a predetermined distance (i.e., cell length), and a frame body including these parts thereon is sandwiched by a pair of cover plates and screwed to be connected. Thus, the length of the spacer can be set so as to determine the cell length.
However, the spacer sandwiched by the pair of light transmitting members may be displaced by a vibration or shock at a time of carrying or installing the flow cell, or due to a pressure, etc., of a sample solution at a time of measurement, and this may result in the flow channel changing in shape, or the spacer may enter an improper position such as a location on an optical path of the measurement light, and there may occur a problem of measurement error.
In addition, in the assembling process of the flow cell, when the spacer is interposed between the light transmitting members, it is difficult to determine where the spacer is positioned with respect to the light transmitting members, and further when the spacer is disposed and sandwiched between the pair of light transmitting members to be fixed, the spacer may be suffer from the problem of being undesirably misaligned. Therefore, it is difficult to assemble the spacer and it is difficult to form the flow channel in a desired shape.